For meMice seem to break a lot more often than keyboards.
For me
Cheap £10 mice seem to last forever (like just standard Dell USB Mouse)
£60 to £130 gaming mice seem to last only a few years
Basically when they break/wear.
Though in keyboards I've lately bought two with smaller timing.
First upgrading from Logitech G710+ to G810 after was it three years to cut down noise and now G815 this year.
(but both at major discounts compared to normal price)
Unfortunately I tend to upgrade mine as soon as something shiny catches my eye.
Wulf
I'm the same, I look at people's setups and spot say, a new mouse or keyboard which piques my interest. I have a tendency to change the setup on a frequent basis, reorganising my desk, going from a triple setup to a single based on the game or work I am doing. Black Friday sales also, picked up some good deals, Logitech MX Mouse for 1/3 of the price etc.